Furnace Not Blowing Air

The blower motor that pushes heated air through the ducts has failed. Burners light, heat exchanger warms, but no air movement means the heat just shuts the system down on high limit.

Set thermostat fan to ON. If blower doesn't spin at all, motor is suspect. Try gently spinning the blower wheel by hand (power OFF) — if stiff or won't turn, bearings are seized. Burning smell from indoor unit = motor windings.

PSC blower motors need a run capacitor to start and operate. Failed cap means motor won't start. ECM (variable speed) motors don't have this issue.

Locate the blower capacitor near the motor. Visual: bulging top, oily leak, scorch marks. Multimeter test: capacitance reading more than 6% below MFD rating means failed.

The high-limit safety switch shut off power to prevent overheating. Limit may have failed closed or may be opening from genuine overheat (no airflow → heat builds up).

Multimeter test across the limit switch terminals. Continuity = good. Open circuit when furnace is cool = failed limit. Tripped limits sometimes self-reset after cooling.

Furnace blower panel has a safety switch that cuts power if the door is not properly seated. Common after service or filter changes when the panel isn't fully closed.

Push firmly on the front blower panel. Listen for a click. If furnace starts working immediately, the door switch was the issue.

The furnace's control board has failed to send power to the blower motor. Often shows erratic blink codes or no LED at all.

Visual inspection: burn marks on the board, swollen capacitors, loose connections. Multimeter at the blower terminal: should show 120V during heat call. If no voltage despite proper ignition sequence, board is suspect.

Very old furnaces (pre-1990s) use a belt between the motor and blower wheel. Belts crack and break with age.

Open the blower compartment. If you see a belt connecting the motor to the blower assembly, inspect for breaks, fraying, or excessive slack. Most modern furnaces are direct-drive (no belt).